This invention relates to a process for the manufacture of vitreous carbon. By carbonizing certain thermosetting polymers, bodies of vitreous carbon can be produced. Vitreous carbon is a hard, corrsion and high temperature resistant material, which has the appearance of black glass. It has been produced for example of pure phenolic resin by heating it carefully in a vacuum, inert or reducing atmosphere so that the transition from resin to vitreous carbon takes place without the body breaking or distorting.
A proper method is described for example in British Pat. No. 956,452. In this method the body of resin is heated at a temperature gradient of 1.degree. C. per hour to 500.degree. C., and then 5.degree. C. per hour until 900.degree. C. is reached. The products obtained are then allowed to cool naturally to room temperature and subsequently re-heated at a gradient of 20.degree. C. per hour until at least 1600.degree. C. is reached. The products obtained are then allowed to cool to room temperature in about 5 hours.
In an alternative method the temperature is raised at a rate of 5.degree. C. per hour until 600.degree. C. is reached, the rate is then increased to 10.degree. C. per hour until 825.degree. C., further increased to 20.degree. C. per hour and the heating continued until at least 1400.degree. C. is reached. The articles are maitained at about this temperature for about 24 hours and then allowed to cool at a temperature gradient of 20.degree. C. per hour.
Several other modified methods have been published and they all have in common relatively low maximum wall thickness of the products if the properties of the material are wanted to be satisfactory. To increase the thickness, a method is described in British Pat. No. 1,266,685, in which the desired body is assembled of thin part bodies, which have been hardened apart. The hardened pieces are glued to joint form with phenolic resin adhesive and are carbonized to vitreous carbon. Pure phenolic resin is used as the starting material also in this method. The carbonization takes place in an argon atmosphere by raising the temperature to 900.degree. C. over a period of 28 days and then heating to 1800.degree. C. under a vacuum of 2 mm Hg over a period of 3 days. At the end of this heating cycle, the body is allowed to cool.
Characteristic of the manufacturing method used today is slowness and hence expensiveness. When using pure resin as the starting material, a rapid rate of heating can not be used because the pressure of the evolving pyrolysis gases from the body becomes too great and the body will be damaged.